Basically, the Sparkle Geforce 6600GT has better performance in terms of performance vs. value. This is because Sparkle Geforce 6600GT is only priced about USD$30 more than the Sparkle Geforce 6600. For that additional price, you'll get a much better performance and the option to SLi. However if you don't plan to spend much, then the Sparkle Geforce 6600 should fit you well and you can overclock it to perform almost as good as the Sparkle Geforce 6600GT.